Does an airliner have to constantly adjust its altitude during the flight........?

Question

.....becase of the consumption of jet fuel.

Answer 1

Altitude is the height of the aircraft. The primary adjustment for the correction of altitude is throttle.

There are four forces on an aircraft in flight: gravity, thrust, drag and lift. Gravity is overcome by lift, and lift is increased by increasing the mass of the air across an airfoil. The amount of air across an airfoil is increased by speeding up the aircraft (increasing thrust).

As an aircraft loses weight throughout the flight, less thrust is required to overcome the gravity.

The trim only serves to correcly orientate the airfoil to the most efficient Angle of Attack (AOA) to maximize its efficiency. Adjusting altitude with trim and not throttle will only slow the aircraft and can induce a stall condition.

Answer 2

The pilot or autopilot would adjust the trim (aka attitude) of the aircraft to keep it a the same flight level.

Answer 3

airliners sometimes perform step climbs. They climb to a certain altitude and cruise there for awhile until they have burn off enough gas to permit them to efficiently cruise at a higher altitude. this is because sometimes, climbing to maximum altitude with full gas may actually be inefficient until some of the gas has been used.

some pilots/airlines also fly faster near the start of their flight and only slow down in the latter part of their flight to make efficient use of gas.

Answer 4

As a matter of fact, yes....but ASIDE from changing altitude in order to take advantage of a lighter weight as fuel is burned off, an airliner, if it is flying at or above 18,000 ft,  DOES have to adjust it's ACTUAL altitude (above sea level) during the flight....but not it's INDICATED altitude!!   [Also, remember that as the weight of an airliner does become less, any change in altitude will be at the discretion of the crew.  But  for various reasons, this is not always done..e.g.  turbulence, adverse winds, etc.]  The reason it WILL adjust it's altitude is because, at and above 18,000 ft.(where most airliners usually fly on long distance flights)  in most countries, the altimeter must be set to 29.92 inches.  Whether the ship is hand flown or on auto pilot, it will be, in effect, constantly trying to maintain an altitude which will compensate for the different sea level pressures along it's flight path.......  Now,  since atmospheric pressure normally will vary from point to point, geographically, during the course of a day, the aircraft might very possibly be actually descending or climbing in an attempt to find the correct pressure altitude; (even though the INDICATED altitude remains the same).....and, since ALL aircraft at those altitudes, in that area, will have their altimeters set to 29.92 inches, they ALL will be making the same corrections........hence, no danger to flight, or air traffic conflicts.